The concept that probiotics are beneficial to gut health has been investigated for a number of years. Studies have demonstrated that probiotics potentially improve gut function through a number of mechanisms including increasing epithelial barrier function (40) and modulation of the immune response (6, 51). There is also evidence that probiotics can prevent colonisation of the gut by pathogens. This can be via mechanisms such as down regulation of virulence factors and inhibition of pathogen adherence to the epithelium (2). For example, lactobacillus species inhibit the adhesion of Enterobacter sakazakii to intestinal mucus by competitive exclusion (32). Other studies demonstrated that some probiotics increase the production of intestinal mucin thus inhibiting pathogen adherence to intestinal epithelial cells (31). Probiotics are also able to produce antimicrobial peptides (bacteriocins) and acids. Collectively, there are numerous probiotic mediated mechanisms that limit pathogen colonisation (33).
Since probiotics may have positive impacts on the gut, their potential effects on other systems, such as the mouth (18) and the urogenital tract (44) have also begun to be investigated. A study in 2001, examining the impact of oral administration of Lactobacilli in a clinical trial of women with bacterial vaginosis, showed that Lactobacilli could indeed inhibit the colonization of uro-epithelial cells by pathogens (44). Recently, the topical application of probiotics to the skin has been investigated in a limited number of studies. Topical application of sonicated Streptococcus salivarius strains to patients suffering from atopic dermatitis resulted in improved barrier function apparently through increasing the level of ceramides in the stratum corneum (13). Topically applied L. plantarum for treatment of infected wounds resulted in improved tissue repair in a mouse burn model and prevention of infection in chronic leg ulcers and burns in humans (41, 42). However, in general the mechanisms underlying these effects are not well understood.
Staphylococcus aureus is both a transient coloniser of skin and a major opportunistic skin pathogen, causing diseases ranging from impetigo to life threatening conditions such as sepsis (25). Previously, our lab demonstrated that the probiotic L. reuteri could protect epidermal keratinocytes from the toxic effects of S. aureus via competitive exclusion of the pathogen from keratinocyte binding sites (43). The inventors have now identified L. rhamnosus GG as a second probiotic with the ability to protect skin cells from the effects of S. aureus. However, L. rhamnosus GG uses multiple mechanisms to protect against infection including inhibition of S. aureus growth, competitive exclusion and displacement of the pathogen from keratinocytes.